Technical Field
The present disclosure relates to bioengineering approaches for producing biofuel and, in particular, to the use of a C1 metabolizing microorganism reactor system for converting C1 substrates, such as methane or methanol, into biomass and subsequently into biofuels, bioplastics, or the like.
Description of the Related Art
With the ever increasing depletion of fossil fuel deposits, the increasing production of greenhouse gases and recent concerns about climate change, substituting biofuels (e.g., ethanol, biodiesel) for fossil fuels has become an industrial focus. But, biofuels generated to date have their own difficulties and concerns. First generation biofuels are derived from plants (e.g., starch; cane sugar; and corn, rapeseed, soybean, palm, and other vegetable oils), but these fuel crops compete with crops grown for human and animal consumption. The amount of farm land available is not sufficient to satisfy both global food and fuel needs. Therefore, second generation biofuels are being produced from, for example, cellulose or algae. But, technical difficulties in production, along with the high cost of production, have not made second generation biofuels any more cost-effective or accessible.
Third or next generation biofuels made from alternative feedstocks (i.e., not sugar, corn, algae) are needed. In this regard, methane is one of the most abundant domestic carbon feedstocks and is sourced primarily from natural gas. The recent rise in domestic production of methane (from 48 bft3/day in 2006 to 65 bft3/day in 2012) has driven the cost of natural gas to record lows (from about $14.00/MMBTU in 2006 to about $2.50/MMBTU in 2012). Domestic natural gas is primarily produced by hydraulic fracturing (“fracking”), but methane can also be obtained from other sources, such as landfills and sewage. In addition, capturing methane sources will have a significant environmental benefit since methane has a 23× greater greenhouse gas contribution relative to CO2.
But, methane's volatility make transportation and direct usage as a fuel problematic. For this reason, there is a strong incentive to convert the gas to a liquid form to allow for easy transport to the point of use. Two main approaches are currently being pursued: liquefaction leading to liquefied natural gas (LNG) and chemical conversion to convert gas-to-liquid (GTL) (Patel, 2005, 7th World Congress of Chemical Engineering, Glasgow, Scotland, UK). The Fischer-Tropsch (F-T) process is currently the most prevalent approach for converting methane from natural gas to higher-order hydrocarbons (Patel, 2005). Note that the F-T process takes syngas as an input which is produced from natural gas by steam reforming (syngas can also be sourced from coal gasification, by high-temperature reaction with water and oxygen). The F-T process yields petroleum products consistent with today's fuel supply, but suffers from a number of drawbacks, including low yields, poor selectivity (making downstream utilization complex), and requires significant capital expenditure and scale to achieve economical production (Spath and Dayton, December 2003 NREL/TP-510-34929). The massive scale required for an F-T plant (more than $2B capital cost for a typical plant [Patel, 2005]) also represents a significant limitation due to the large amount of methane feedstock required to supply continuous operation of such a plant. As methane transportation is prohibitively expensive in most cases, such a plant must be co-located with either a large gas source or a pipeline. An additional cost and scaling factor is the economics of gas-scrubbing technologies (Spath and Dayton, 2003), as F-T catalysts are highly sensitive to common contaminants in natural gas that survive the syngas conversion process.
F-T plants have been in operation semi-continuously since 1938. Several companies are currently investigating introduction of new plants given the current availability and price of methane discussed above. However, despite significant research and development over the last 70+ years, the limitations of F-T technology prevent broad adoption of commercial GTL processes. The requirements for ready access to large volumes of clean gas, combined with massive capital investment, currently limit natural gas based F-T plants to successful operation in only a few locations world-wide (Spath and Dayton, 2003). The high minimum processing requirement for a GTL or LNG plant, combined with the high cost of transport, result in smaller methane sources being referred to as ‘stranded’ gas (for example, natural gas produced at off-shore oil wells, or methane off-gas from landfills). In the current absence of efficient small-scale conversion technologies, such stranded gas sources are typically vented to atmosphere or flared, as methane accumulation presents a significant safety risk.
In view of the limitations associated with the production of first, second and next generation biofuels, there is clearly a need in the art for new methods of efficiently and cost-effectively producing alternative fuels without taxing the environment or competing with food production. The present invention solves this problem by providing efficient and cost-effective methods for producing biofuels and other products using bioengineering.